1. Field of the Invention
The present invention relates to signal processing for thermal printers.
2. Description of the Prior Art
Some thermal printer apparatus use a dye transfer process. In this process, a carrier containing a dye is disposed between a receiver, such as paper, and a print head formed of for example a plurality of individual thermal heat producing elements often referred to as heating elements. The receiver and carrier are generally moved relative to the print head which is fixed. When a particular heating element is energized, it is heated and causes dye to transfer (e.g. by sublimation) from the carrier to an image pixel in the receiver. The density, or darkness, or the printed dye is a function of the temperature of the heating element and the time the carrier is heated. In other words, the heat delivered from the heating element to the carrier causes dye to transfer to an image pixel of a receiver. The amount of dye is directly related to the amount of heat transferred to the carrier.
Thermal dye transfer printer apparatus offer the advantage of true "continuous tone" dye density transfer. By varying the heat applied by each heating element to the carrier, a variable dye density image pixel is formed in the receiver.
Continuous tone thermal printers are used to print color images. First a cyan image is printed and then magneta and yellow images are superimposed on the cyan image to form a colored image apparatus for making color images is shown in FIGS. 1-3 of this disclosure. Any order of printing can be used.
Many commercially available apparatus, produce color images in which the color pictorial information in such color images need to be enhanced. Signal processing algorithms are presently available but they are expensive and time consuming and tend to be quite complex.